CBSE Class 10 Science: Electricity (CBSE) — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: State Ohm's Law. Draw V-I graph for a resistor following Ohm's Law.
  Ans: Ohm's Law: At constant temperature, the current through a conductor is directly proportional to the potential difference across its ends. V = IR. The V-I graph is a straight line passing through the origin with slope = R (resistance). The steeper the line, the greater the resistance.
• Q: Derive the expression for equivalent resistance when resistors are connected (i) in series, (ii) in parallel.
  Ans: (i) Series: Same current I through all resistors. V = V₁ + V₂ + V₃. IR_eq = IR₁ + IR₂ + IR₃. R_eq = R₁ + R₂ + R₃. (ii) Parallel: Same voltage V across all resistors. I = I₁ + I₂ + I₃. V/R_eq = V/R₁ + V/R₂ + V/R₃. 1/R_eq = 1/R₁ + 1/R₂ + 1/R₃. In series: R_eq > any individual R. In parallel: R_eq < smallest R.
• Q: What is the heating effect of electric current? State Joule's law of heating.
  Ans: When current flows through a resistor, electrical energy is converted to heat energy. This is the heating effect of current. Joule's law: H = I²Rt. Heat produced is: (1) directly proportional to square of current (I²), (2) directly proportional to resistance (R), (3) directly proportional to time (t). Applications: electric heater, iron, toaster, fuse.

Long Answer / Application Questions (4-6 Marks)

• Q: An electric iron consumes energy at the rate of 840 W when heating is at maximum and 360 W when heating is at minimum. Find the current and resistance in each case (V = 220 V).
  Ans: At maximum: P = 840 W, V = 220 V. I = P/V = 840/220 = 3.82 A. R = V/I = 220/3.82 = 57.6 Ω. At minimum: P = 360 W. I = P/V = 360/220 = 1.64 A. R = V/I = 220/1.64 = 134.15 Ω. Higher resistance at minimum heating means less current and less heat produced.

Exam Tips for This Chapter

• Revise all definitions and laws from Electricity (CBSE) — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Electricity (CBSE) — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Electricity (CBSE) carries 8-12 marks in the board exam